Cationic conductor

ABSTRACT

The present invention provides a cationic conductor comprising a block copolymer comprising: a polymer moiety having a structural unit represented by formula (1):  
                 
 
wherein R represents an organic group obtained via polymerization of monomer compounds having polymerizable unsaturated linkages; Q represents an n+1-valence organic group bonded to R through a single bond; Z represents a functional group capable of forming an ionic bond to or having coordination ability to a cation; M k+  represents a k-valence cation; and n and m are each independently an integer of 1 or larger, provided that Z forms an ionic or coordination bond to a cation; and a polymer moiety having addition polymerizable monomers.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an ionic conductive organic electrolyteand an ionic conductive polymer electrolyte.

2. Description of Related Art

Advances in electronics have allowed the performances of electronicdevices to be enhanced, and electronic devices have been miniaturizedand made portable. Accordingly, secondary batteries with high energydensity have been needed as power sources for such devices. In responseto such need, nonaqueous electrolyte system secondary batteries withsignificantly enhanced energy density, i.e., lithium ion secondarybatteries with organic electrolytic solution (hereafter simply referredto as “lithium batteries”), have been developed, and they have becomewidely prevalent in recent years. Lithium batteries use, for example,lithium metal complex oxides such as lithium-cobalt complex oxides aspositive electrode active materials. They primarily use as theirnegative electrode active materials multilayered carbon materialscapable of intercalating lithium ions in the layered structure(formation of lithium intercalation compounds) and deintercalatinglithium ions out of the layered structure.

Lithium batteries use a combustible organic electrolytic solution. Thus,securing of safety in the case of overuse, such as overcharge orover-discharge, is becoming difficult with the enhancement in energydensity of the batteries. Accordingly, lithium polymer batteries inwhich the combustible organic electrolytic solution has been replacedwith a solid lithium-ionic conductive polymer were developed.

A mechanism of an ionic conductive polymer for conducting ions that hasheretofore been examined is known to occur in conjunction with themotion of a polymer molecular chain. Ionic conductivity is governed bymobility of the molecular chain and by motion of a molecular chainhaving high activation energy, which is required for segmental motion.Thus, ionic conductivity at room temperature is approximately 10⁻⁴Scm⁻¹, but it becomes significantly lower as the temperature drops.

The present inventors conceived of the application of single bondrotation with low activation energy to a mechanism for conducting ionsthat is not governed by motion of a molecular chain.

An organic group having a functional group, which is a ligandcoordinated to a lithium ion, is bonded to another organic group througha single bond, and thus, free rotation can be realized in a widetemperature range. This rotation allows lithium ion exchange betweenadjacent similar functional groups, and ions are conducted via suchexchange. This mechanism of conducting ions has allowed realization ofthe preparation of a polymer electrolyte having excellent temperaturedependence (JP Patent Publication (Kokai) No. 2004-6273 A).

SUMMARY OF THE INVENTION

Polymerization of a monomer having an organic group that has afunctional group that is a ligand coordinated to a lithium ion andaffects ionic conduction has allowed realization of the production of anionic conductor that utilizes single bond rotation. In order to put itto practical use, however, ionic conductivity must be enhanced.

In order to solve such problem, the following cationic conductorscomprising polymer electrolytes are used.

A cationic conductor comprising a block copolymer comprising: a polymermoiety having a structural unit represented by formula (1):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Qrepresents an n+1-valence organic group bonded to R through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; and n and m are each independently an integer of 1 orlarger, provided that Z forms an ionic or coordination bond to a cation;and a polymer moiety having addition polymerizable monomers.

A cationic conductor comprising an alternating copolymer represented byformula (3):

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; Q represents an n+1-valence organic group bondedto R₁ through a single bond; Z represents a functional group capable offorming an ionic bond to or having coordination ability to a cation;M^(k+) represents a k-valence cation; n and m are each independently aninteger of 1 or larger; and i represents the polymerization degree,provided that Z forms an ionic or coordination bond to a cation.

A cationic conductor composed of a mixture of a polymer represented byformula (5):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Qrepresents an n+1-valence organic group bonded to R through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; and n and m are each independently an integer of 1 orlarger, provided that Z forms an ionic or coordination bond to a cation;and a different type of polymer.

According to the present invention, an electrolyte having excellentionic conductivity can be obtained.

This specification includes part or all of the contents as disclosed inthe specifications of Japanese Patent application No. 2004-189098, whichare the base of the priority claim of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a ratio of reaction rates for two types of reactions wherea block copolymer is formed.

FIG. 2 shows a ratio of reaction rates for two types of reactions wherean alternating copolymer is formed.

FIG. 3 shows the results of comparison of the cationic conductorprepared in Examples 1 and 3 of the present invention and a conventionalcationic conductor via reciprocal plotting of the ionic conductivity andthe temperature.

FIG. 4 shows the lithium secondary battery prepared in Example 7.

Hereafter, embodiments of the present invention are described.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

According to an embodiment of the present invention, a cationicconductor comprises a block copolymer comprising: a polymer moietyhaving a structural unit represented by formula (2):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Srepresents an organic group bonded to R; T represents an n+1-valenceorganic group bonded to S through a single bond; Z represents afunctional group capable of forming an ionic bond to or havingcoordination ability to a cation; M^(k+) represents a k-valence cation;and n and m are each independently an integer of 1 or larger, providedthat Z forms an ionic or coordination bond to a cation; and a polymermoiety having addition polymerizable monomers.

In the case of the cationic conductor of the present example, organicgroup S is bonded to organic group T through a single bond, and T freelyrotates around this single bond. The compound of the present exampleexhibits cationic conductivity via easy migration and exchange ofcations M^(k+) coordinated to functional group Z between adjacentorganic groups Ts.

It is important that a bond between organic groups S and T be a singlebond. A bond between organic groups R and S is not limited to a singlebond.

According to an embodiment of the present invention, a cationicconductor comprises a block copolymer comprising: a polymer moietyhaving a structural unit represented by formula (7), corresponding toformula (2) wherein T is an aryl group:

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; S is anorganic group bonded to R and to a Z-bonded benzene derivative through asingle bond; Z represents a functional group capable of forming an ionicbond to or having coordination ability to a cation; M^(k+) represents ak-valence cation; and n and m are each independently an integer of 1 orlarger, provided that Z forms an ionic or coordination bond to a cation;and a polymer moiety having addition polymerizable monomers.

According to a further embodiment of the present invention, a cationicconductor comprises a block copolymer comprising: a polymer moietyhaving a structural unit represented by formula (8), corresponding toformula (7) wherein S represents an amide group in which N (a nitrogenatom) is bonded to R and C (a carbon atom) is bonded to the aryl group:

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Zrepresents a functional group capable of forming an ionic bond to orhaving coordination ability to a cation; M^(k+) represents a k-valencecation; and n and m are each independently an integer of 1 or larger,provided that Z forms an ionic or coordination bond to a cation; and apolymer moiety having addition polymerizable monomers.

In the case of a polymer electrolyte comprising an organicgroup-containing monomer that affects ionic conduction, a polymermolecular chain composed of continuing organic groups that affect ionicconduction is hard. Thus, it was deduced that ionic conduction would beinhibited at the interface between domains of the polymer molecularchain, which would result in deteriorated ionic conductivity.

Enhancement in ionic conductivity was attempted by copolymerizing such amonomer with a styrene monomer capable of a similar form of additionpolymerization; however, no satisfactory effect was attained. Since thecopolymer thus obtained is a random copolymer with an irregular sequenceconsisting of an organic group affecting ionic conduction and a styrenemonomer that was used for copolymerization, it was deduced that amechanism of conducting ions via single bond rotation would not functionsufficiently. Thus, it was considered that sequence regulation must becarried out in a polymer of the organic group.

In general, a monomer that is subjected to addition polymerizationexhibits changes in reactivity upon polymerization due to a type of afunctional group that is bonded to an unsaturated hydrocarbon group ofthe monomer. When such monomer is copolymerized with a different type ofmonomer, different types of monomers may be irregularly or regularlyaligned due to differences in reactivity. The Q-e value can bedetermined concerning the reactivity of an addition polymerizablemonomer. Q represents a degree of resonance stabilization of themonomer, and e indicates the relative electric charge of unsaturatedlinkage.

Two types of monomers are designated as M₁ and M₂, and the Q-e valuesthereof are designated as Q₁·e₁ and Q₂·e₂, respectively. A radical isgenerated at the end of the polymer chain that is elongated via radicalpolymerization, and polymerization takes place when an unsaturatedlinkage of a monomer reacts to the radical. Where a radical at theterminus of a propagating polymer chain is generated from M₁ and an M₁monomer is polymerized therewith, the reaction rate thereof isdesignated as k₁₁. Where a radical at the terminus of an elongatingpolymer chain is generated from M₁ and M₂ is polymerized therewith, thereaction rate thereof is designated as k₁₂. The ratio r₁ of the abovereaction rates is represented by equation 1. Similarly, where a radicalat the terminus of an elongating polymer chain is generated from M₂ andan M₁ or M₂ monomer is polymerized therewith, reaction rates thereof aredesignated as k₂₁ and k₂₂, respectively. The ratio r₂ is represented byequation 2.

The ratio of reaction rates r₁ and r₂ can be represented by theaforementioned Q-e values (equations 3 and 4).

The form of a copolymer can be regulated by monomer type selection forsuch copolymerization. When the conditions r₁>1 and r₂<1 are satisfied,M₁−M₁ and M₂−M₂ reactions are facilitated. Thus, a block copolymercomprising a recurring unit consisting of a structural unit ofconsecutively bound M₁ monomers and a structural unit of consecutivelybound M₂ monomersis generated. The ratios of reaction rates r₁ and r₂when such structural unit is realized are r₁×r₂<1, r₁>1 and 0<r₂<1, andparticularly preferably r₁×r₂<1, r₁>20 and 0<r₂<0.05, concerning a blockcopolymer (FIG. 1).

A block copolymer is comprised of a polymer moiety consisting ofmonomers including organic groups that affect conduction of ions alignedwith a polymer moiety consisting of monomers to be copolymerized. It wasdeduced that an organic group that affects ionic conduction inhibitedionic conduction at the interface between domains of a continuingpolymer molecular chain in the case of a homopolymer..

In contrast, it is assumed that a space between domains of the polymermolecular chain of a block copolymer, which is composed of continuingorganic groups that affect ionic conduction, is bonded with the aid of apolymer moiety consisting of monomers used for copolymerization. Thus,ionic conductivity can be enhanced by the effects of assisting ionicconduction at the interface between domains or segmental motion of thepolymer molecule realized by functioning as a plasticizer on a polymermolecular chain.

The structure of such block copolymer can be assayed via the nuclearmagnetic resonance method. Since different types of additionpolymerizable functional groups form a polymer, the structure of thecopolymer can be determined by separately observing the peaks derivedfrom the different functional groups.

In the present example, organic group T has at least 1 functional groupZ that can be coordinated to a cation. When functional group Z is oxygen(O⁻), examples of an organic group include phenolate anions such ashydroxy phenyl and dihydroxy phenyl groups. Alternatively, an oxygenatom in such anion may be substituted with a sulfur atom, i.e., a groupin the form of thiophenyl or dithiophenyl may be used. When functionalgroup Z is methoxy (—OCH₃), an organic group can be an alkoxy phenylgroup such as a methoxy phenyl or dimethoxy phenyl group. An alkyl groupsuch as a methoxy or ethoxy group can be used as an alkoxy group (—OR,wherein R represents an alkyl group). If the size of an alkyl group isenlarged, single bond rotation may be inhibited, or solubility of thecationic conductor may be adversely affected, which may result indeteriorated workability. An alkylthio group that is prepared bysubstituting an oxygen atom with a sulfur atom in an alkoxy group mayalso be used. Also, functional group Z can also be used in the form ofester (—O—C(═O)—R, —C(═O)O—R), an amino group (—NR₁R₂), an acyl group(—C(═O)—R), or carbonate (—O—C(═O)—OR).

Butyllithium, azobisisobutyronitrile, or peroxides such as benzoylperoxide or t-hexyl peroxypivalate can be used as an initiator forpolymerization where a polymer is generated. t-Hexyl peroxypivalate isparticularly preferable.

In the present example, organic group R has a styrene skeleton.Originally, however, such organic group R is not particularly limited,and a variety of organic groups, such as a saturated hydrocarboncompound, an unsaturated hydrocarbon compound, or an aromatichydrocarbon compound, can be employed. Such organic group is not limitedto a hydrocarbon compound, and an organic group may contain elements,such as nitrogen, sulfur, or oxygen. Alternatively, part of such organicgroup may be substituted by halogen. The molecular weight thereof is notlimited, and low-molecular-weight to high-molecular-weight compounds canbe employed. A high-molecular-weight compound may be a polymer oflow-molecular-weight monomers. The number of Z that is bonded to organicgroup T is not particularly limited, and substitution of at least onegroup per molecule represented by a general formula is sufficient.Alternatively, a plurality of monomers may be substituted.Polymerization can be carried out via addition polymerization.

When an addition polymerizable functional group of an ionic conductivefunctional group-containing monomer is a styryl group, vinyl acetate,isobutyrene, isobutyl vinyl ether, and ethylene are preferably used asmonomers that are subjected to copolymerization.

In the present example, lithium is employed as a cation. Alkali metalions such as sodium or potassium, alkaline earth metals such asmagnesium, or a hydrogen ion can also be used. Among them, lithium ionsare most preferable.

Lithium salts can also be used as lithium ion sources. Examples oflithium salts include LiN(CF₃CF₂SO₂)₂, LiN(CF₃SO₂)₂, LiClO₄, LiPF₆,LiBF₄, and LiAsF₆, and they can be used solely or in combinations of twoor more. LiN(CF₃CF₂SO₂)₂ is particularly preferable. Preferably, atleast 1 equivalent of lithium ions is added relative to one organicgroup Z, which is involved with lithium conduction, in terms of a molarproportion.

A concrete method 1 for synthesizing a cationic conductor consisting ofa block copolymer comprising a polymer moiety having a structural unitrepresented by formula (8) and a polymer moiety having a monomer unitfor copolymerization is described.

A monomer 1, i.e., (N-(di(2-aminoethyl)aminoethyl)-2,6-dimethoxy benzoicacid amide, (50 g) obtained by the method disclosed in JP PatentPublication No. 2004-6273 A and 4.9 ml of vinyl acetate are dissolved in0.4 dm³ of tetrahydrofuran, 1 cm³ of hexane solution containing 70 wt %t-hexyl peroxypivalate is added thereto, and the mixture is stirred at70° C. to obtain a block copolymer. The resulting copolymer (1 g) and 3g of LiN(CF₃CF₂SO₂)₂ are dissolved in 20 ml of N-methylpyrrolidone, theresulting solution is cast on a poly(tetrafluoroethylene) sheet, thesheet is subjected to vacuum drying at 80° C., and a cast film of ablock copolymer having a thickness of 100 μm is prepared.

This cast film is inserted between stainless (SUS 304) electrodes withdiameters of 15 mm to prepare a test cell. An amplitude voltage of 10 mVis applied to this cell at room temperature to measure a.c. impedance.The frequency range is between 1 Hz and 1 MHz. Based on the reciprocalof the bulk ohmic value obtained by the measurement of a.c. impedance,ionic conductivity is determined. Ionic conductivity was found to be1.5×10⁻⁴ Scm⁻¹ at room temperature, which was higher than that of thepolymer electrolyte prepared in Comparative Example 1.

Regulation of the polymer molecular chain sequence of an organic groupthat affects ionic conduction can enhance ionic conductivity of thepolymer electrolyte.

EXAMPLE 2

According to an embodiment of the present invention, a cationicconductor comprises an alternating copolymer comprising an organic grouprepresented by formula (4):

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; S represents an organic group bonded to R; Trepresents an n+1-valence organic group bonded to S through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; n and m are each independently an integer of 1 orlarger; and i represents the polymerization degree, provided that Zforms an ionic or coordination bond to a cation.

In the case of the cationic conductor of the present example, organicgroup S is bonded to organic group T through a single bond, and T freelyrotates around this single bond. The compound of the present exampleexhibits cationic conductivity via easy migration and exchange ofcations M^(k+) coordinated to functional group Z between adjacentorganic groups Ts.

It is important that a bond between organic groups S and T be a singlebond. A bond between organic groups R and S is not limited to a singlebond.

According to an embodiment of the present invention, a cationicconductor comprises an alternating copolymer having an aryl grouprepresented by T in formula (4) and represented by formula (9):

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; S represents an organic group bonded to R₁ and toa Z-bonded benzene derivative through a single bond; Z represents afunctional group capable of forming an ionic bond to or havingcoordination ability to a cation; M^(k+) represents a k-valence cation;n and m are each independently an integer of 1 or larger; and irepresents the polymerization degree, provided that Z forms an ionic orcoordination bond to a cation.

According to another embodiment of the present invention, a cationicconductor comprises an alternating copolymer represented by formula(10), corresponding to formula (9) wherein S is an amide group in whichN (a nitrogen atom) is bonded to R and C (a carbon atom) is bonded tothe aryl group

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; Z represents a functional group capable of formingan ionic bond to or having coordination ability to a cation; M^(k+)represents a k-valence cation; n and m are each independently an integerof 1 or larger; and i represents the polymerization degree, providedthat Z forms an ionic or coordination bond to a cation.

In the case of a polymer electrolyte consisting of an organicgroup-containing monomer that affects ionic conduction, rotation at thetime of ionic conduction is inhibited due to steric crowding in thefunctional group. This was assumed to lower ionic conductivity.

As described in Example 1, monomer type selection for copolymerizationenables regulation of the form of the copolymer. When the valuesrepresented by r₁ and r₂ are excessively small and close to 0, reactionbetween different types of monomers is more likely to proceed comparedto the case where reaction takes places between monomers of the sametype. An alternating copolymer in which M₁ and M₂ are substantiallyregularly and alternately aligned is generated thereupon.

By selecting an appropriate monomer type for copolymerization, analternating copolymer in which an organic group-containing monomer thataffects ionic conduction is alternately aligned with a monomer to becopolymerized can be obtained. In such a case, a distance betweenorganic groups that affect ionic conduction may be regulated to reducethe steric crowding in the functional groups and accelerate the rotationupon ionic conduction. Thus, enhancement in ionic conductivity can beexpected.

Ratios of reaction rates r₁ and r₂ where such alternating copolymer isobtained are preferably in the ranges of 0<r₁<0.5 and 0<r₂<0.3, andparticularly preferably in the range of 0<r₁<0.3 and 0<r₂<0.1 (FIG. 2).

Such alternating copolymer structure can be confirmed via the nuclearmagnetic resonance method. Since different types of additionpolymerizable functional groups are alternately aligned, the alternatingcopolymer structure can be determined based on the fact that peaksderived from such functional groups are uniform and of a single type.

When a polymerizable functional group of a monomer having a functionalgroup that affects ionic conduction is a styryl group, a monomer, suchas maleic anhydride, N-phenyl maleimide, methyl maleic anhydride,citraconic anhydride, acrylonitrile, diethyl fumarate, vinylidenecyanide, p-nitrostyrene, methyl vinyl ketone, or methacrylonitrile, ispreferably used for copolymerization.

A concrete method 1 for synthesizing a cationic conductor consisting ofan alternating copolymer having a structural unit represented by formula(8) and a monomer for copolymerization is described.

A monomer 1 (50 g) and 9 g of N-phenyl maleimide are dissolved in 0.4dm³ of tetrahydrofuran, 1 cm³ of hexane solution containing 70 wt %t-hexyl peroxypivalate is added thereto, and the mixture is stirred at70° C. to obtain an alternating copolymer. The resulting copolymer (1 g)and 3 g of LiN(CF₃CF₂SO₂)₂ are dissolved in 20 ml ofN-methylpyrrolidone, the resulting solution is cast on apoly(tetrafluoroethylene) sheet, the sheet is subjected to vacuum dryingat 80° C., and a cast film of an alternating copolymer having athickness of 100 μm is prepared.

This cast film was subjected to measurement of a.c. impedance in thesame manner as in Example 1 to determine ionic conductivity. Ionicconductivity was found to be 4.8×10⁻⁵ Scm⁻¹ at room temperature.

EXAMPLE 3

A monomer 1 (50 g) and 11.8 ml of acrylonitrile are dissolved in 0.2 dm³of tetrahydrofuran, 1 cm³ of hexane solution containing 70 wt % t-hexylperoxypivalate is added thereto, and the mixture is stirred at 70° C. toobtain an alternating copolymer. The resulting copolymer (1 g) and 3 gof LiN(CF₃CF₂SO₂)₂ are dissolved in 20 ml of N-methylpyrrolidone, theresulting solution is cast on a poly(tetrafluoroethylene) sheet, thesheet is subjected to vacuum drying at 80° C., and a cast film of analternating copolymer having a thickness of 100 μm is prepared.

This cast film was subjected to measurement of a.c. impedance in thesame manner as in Example 1 to determine ionic conductivity. Ionicconductivity was found to be 1.8×10⁻⁴ Scm⁻¹ at room temperature, whichwas higher than that of the polymer electrolyte prepared in ComparativeExample 1.

EXAMPLE 4

According to an embodiment of the present invention, a cationicconductor is composed of a mixture of: a polymer represented by formula(6):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Srepresents an organic group bonded to R; T represents an n+1-valenceorganic group bonded to S through a single bond; Z represents afunctional group capable of forming an ionic bond to or havingcoordination ability to a cation; M^(k+) represents a k-valence cation;and n and m are each independently an integer of 1 or larger, providedthat Z forms an ionic or coordination bond to a cation; and a differenttype of polymer.

In the case of a polymer electrolyte consisting only of an organicgroup-containing monomer that affects ionic conduction, a polymermolecular chain composed of continuing organic groups that affect ionicconduction is hard. Thus, it was deduced that inhibition of ionicconduction at the interface between domains of the polymer molecularchain would deteriorate ionic conductivity. In order to enhanceconductivity, a polymer blend comprising polymers having differentproperties may be effective.

A “polymer blend” is prepared by mixing polymers having differentproperties. It is deduced that, via such procedure, a space betweendomains of a polymer molecular chain composed of continuing organicgroups that affect ionic conduction be bridged and bonded with the aidof polymers used for blending. Therefore, enhanced ionic conductivitycan be expected because of the effects of assisting ionic conduction atthe interface between domains.

A polymer blend preferably comprises polymers, such as polyvinylacetate, polymethyl methacrylate, polymethyl acrylate, and polylaurylmethacrylate.

A homopolymer (3.0 g) comprising the monomer 1 obtained by the methoddisclosed in JP Patent Publication No. 2004-6273 A is dissolved in 60 mlof NMP. Polyvinyl acetate (0.3 g) is dissolved in 10 ml of NMP. Thesesolutions are mixed with 8.2 g of LiN(CF₃CF₂SO₂)₂ to prepare a solution.The resultant is cast on a poly(tetrafluoroethylene) sheet, the sheet issubjected to vacuum drying at 80° C., and a cast film of a polymer blendhaving a thickness of 100 μm is prepared.

This cast film was subjected to measurement of a.c. impedance in thesame manner as in Example 1 to determine ionic conductivity. Ionicconductivity is deduced to be higher at room temperature than that ofthe polymer electrolyte prepared in Comparative Example 1.

EXAMPLE 5

FIG. 4 shows a cross section of a lithium battery using a cationicconductive polymer electrolyte according to an embodiment of the presentinvention.

A lithium ionic conductive polymer electrolyte of the present example isa complex of a polymer and a lithium salt. Such electrolyte can beobtained by dissolving a monomer having an organic group that affectsionic conduction, a monomer for copolymerization, and a lithium salt inan organic solvent, subjecting the resulting solution to polymerization,and then removing an organic solvent. Alternatively, a block copolymeror an alternating copolymer is dissolved in an organic solvent, or apolymer having organic group-containing monomers that affect ionicconduction is dissolved in an organic solvent for a different type ofpolymer. A lithium salt is added thereto, and an organic solvent is thenremoved. Thus, a lithium ionic conductive polymer electrolyte can alsobe obtained.

A polymer electrolyte is prepared in the form of a sheet when it is usedas an electrolyte for a lithium battery and is made to function as aseparator between positive and negative electrodes. Such sheet-likepolymer electrolyte can be obtained by dissolving a monomer having anorganic group that affects ionic conduction, a monomer forcopolymerization, and a lithium salt in an organic solvent, subjectingthe resulting solution to addition polymerization by heating, andremoving an organic solvent by evaporation. Alternatively, a blockcopolymer or an alternating copolymer is dissolved in an organicsolvent, or a polymer having organic group-containing monomers thataffect ionic conduction is dissolved in an organic solvent for adifferent type of polymer. A lithium salt is added thereto, theresultant is cast on a poly(tetrafluoroethylene) sheet, and an organicsolvent is then removed by evaporation. Thus, a polymer electrolyte canalso be obtained.

Examples of an organic solvent that dissolves polymer electrolyte andlithium salt include N-methylpyrrolidone, dimethylformamide, toluene,propylene carbonate, and γ-butyrolactone, which thoroughly dissolvelithium salt but do not react with a polymer.

A positive active material that reversibly intercalates anddeintercalates lithium may be at least one of the following: a layeredcompound such as lithium cobalt oxide (LiCoO₂) or lithium nickel oxide(LiNiO₂); a layered compound in which at least one kind of transitionmetal has been substituted; lithium manganese oxide (Li_(1+X)Mn_(2−X)O₄,where X=0 to 0.33); Li_(1+X)Mn_(2−X−Y)M_(Y)O₄, where M is at least onemember selected from the group of metals consisting of Ni, Co, Cr, Cu,Fe, Al, and Mg, X=0 to 0.33, and Y=0 to 1.0, and 2−X−Y>0; LiMnO₃,LiMn₂O₃, LiMnO₂, or LiMn_(2−X)M_(X)O₂, where M is at least one memberselected from the group of metals consisting of Co, Ni, Fe, Cr, Zn, andTa, and X=0.01 to 0.1; Li₂Mn₃MO₈, where M is at least one memberselected from the group of metals consisting of Fe, Co, Ni, Cu, and Zn);a copper-lithium oxide (Li₂CuO₂); an oxide of vanadium such as LiV₃O₈,LiFe₃O₄, V₂O₅, V₆O₁₂, VSe, or Cu₂V₂O₇; a disulphide compound; a mixturecontaining Fe₂(MoO₄)₃ etc; polyaniline; polypyrrole; and polythiophene.

A negative active material that reversibly intercalates anddeintercalates lithium include: an easily graphitizable materialobtained from natural graphite, petroleum coke, or coal pitch coke thathas been subjected to heat treatment at high temperatures of 2500° C. orhigher; mesophase carbon or amorphous carbon; carbon fiber; a lithiummetal; a metal that alloys with lithium; or a carbon particle carrying ametal on the surface thereof. Examples thereof include metals or alloysselected from the group consisting of lithium, aluminum, tin, silicon,indium, gallium, and magnesium. These metals or their oxides may beutilized for the negative electrode active materials.

A battery with polymer electrolyte of the present example comprises apositive electrodes prepared from the aforementioned positive activematerial and a negative electrode prepared from the aforementionednegative active material separated by a sheet-like polymer electrolyte.Also, positive and negative electrodes containing a polymer electrolytecan be prepared in order to enhance adhesion between a positive ornegative active material and a polymer electrolyte. In such a case, amonomer having an organic group that affects ionic conduction, a monomerfor copolymerization, and a lithium salt are dissolved in an organicsolvent, the resulting solution is cast on the positive and negativeelectrodes, and heat polymerization is then carried out. Alternatively,a copolymer comprising a lithium salt and an organic group that affectsionic conduction is dissolved in an organic solvent, the resultingsolution is cast on the electrodes, and an organic solvent is thenremoved. Thus, such electrodes can be obtained. The thus-obtainedpositive and negative electrodes may be bonded to each other to obtain abattery with polymer electrolyte.

Such battery with polymer electrolyte is suitably mounted on electricequipment as shown below.

For example, such polymer electrolyte may be utilized for lithiumsecondary batteries as the electric power supplies for: electricautomobiles; electric bicycles; personal computers; cellular phones;digital cameras; camcorders; portable minidisc players; personal digitalassistants; wrist watches; radios; electronic personal organizers;electric tools; vacuum cleaners; toys; elevators; robots for emergencypurposes; walking-aid machines for healthcare purposes; wheelchairs forhealthcare purposes; moving beds for healthcare purposes; emergencyelectric supplies; load conditioners; and electric power storage systems(Example 8). Since no electrolytic fluid is used, it is expected thatthe safety level is enhanced and need of a protection circuit iseliminated. Thus, lithium secondary batteries can be used asrechargeable batteries for household use, the size thereof can beenlarged, and thus, they are suitable as dispersed power sources forhousehold and regional use. The performance level can be maintained atlow temperature no different from that at room temperature, fluid doesnot leak at high temperatures, and thus, the batteries can be used in awide temperature range. Accordingly, they may also be utilized as thepower supplies for military, space-exploration, or emergency purposes,as well as for consumer applications. Employing a hydrogen ion as M^(k+)in formulae (1) to (6) enables the use thereof as an electrolytic filmof a fuel cell.

COMPARATIVE EXAMPLE 1

A method for synthesizing a cationic conductor using a homopolymercomprising the monomer 1 obtained by the method disclosed in JP PatentPublication (Kokai) No. 2004-6273 A is described.

The obtained monomer 1 (140 g) was dissolved in 5 dm³ oftetrahydrofuran, 0.4 g of azobisisobutyronitrile was added thereto, andthe mixture was stirred at 65° C. This reaction solution was addeddropwise to 10 dm³ of n-hexane to obtain a polymer electrolyte 3(poly(N-(4-vinylphenyl)-2,6-dimethoxy benzoic acid amide)). Theresulting polymer electrolyte 3 (50 g) was dissolved in 2 dm³ ofN-methylpyrrolidone, and 98 g of lithium trifluorosulfonimide salt wasadded thereto, followed by mixing. Thereafter, the resultant was cast ona poly(tetrafluoroethylene) sheet and subjected to vacuum drying at 60°C. to obtain a cast film having a thickness of 100 μm. With the use ofthis cast film, a test cell was prepared in the same manner as inExample 1 to determine ionic conductivity. Ionic conductivity was foundto be 1.4×10⁻⁴ Scm⁻¹.

COMPARATIVE EXAMPLE 2

A.c. impedance was measured in order to examine the temperaturedependence of the ionic conductivity using the test cell prepared inComparative Example 1. The test cell was allowed to stand in athermostat maintained at the given temperature level for 30 minutes, andthe measurement was carried out in a manner such that the cell was setin the thermostat. Ionic conductivity was determined in the same manneras in Comparative Example 1.

All the publications, patents and patent applications cited herein areincorporated herein by reference in their entirely.

1. A cationic conductor comprising a block copolymer comprising: apolymer moiety having a structural unit represented by formula (1):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Qrepresents an n+1-valence organic group bonded to R through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; and n and m are each independently an integer of 1 orlarger, provided that Z forms an ionic or coordination bond to a cation;and a polymer moiety having addition polymerizable monomers.
 2. Acationic conductor comprising a block copolymer comprising: a polymermoiety having a structural unit represented by formula (2):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Srepresents an organic group bonded to R; T represents an n+1-valenceorganic group bonded to S through a single bond; Z represents afunctional group capable of forming an ionic bond to or havingcoordination ability to a cation; M^(k+) represents a k-valence cation;and n and m are each independently an integer of 1 or larger, providedthat Z forms an ionic or coordination bond to a cation and R is a styrylgroup before polymerization; and a polymer moiety comprising vinylacetate, isobutylene, isobutyl vinyl ether, and ethylene as additionpolymerizable monomers.
 3. A cationic conductor comprising analternating copolymer represented by formula (3):

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; Q represents an n+1-valence organic group bondedto R₁ through a single bond; Z represents a functional group capable offorming an ionic bond to or having coordination ability to a cation;M^(k+) represents a k-valence cation; n and m are each independently aninteger of 1 or larger; and i represents the polymerization degree,provided that Z forms an ionic or coordination bond to a cation.
 4. Acationic conductor comprising an alternating copolymer represented byformula (4):

wherein R₁ and R₂ each independently represent an organic group obtainedvia polymerization of monomer compounds having addition polymerizableunsaturated linkages; R₁ is a styryl group before polymerlyzation; R₂ isa product of polymerization of monomers selected from the groupconsisting of maleic anhydride, N-phenyl maleimide, methyl maleicanhydride, citraconic anhydride, acrylonitrile, diethyl fumarate,vinylidene cyanide, p-nitrostyrene, methyl vinyl ketone, andmethacrylonitrile; S represents an organic group bonded to R; Trepresents an n+1-valence organic group bonded to S through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; n and m are each independently an integer of 1 orlarger; and i represents the polymerization degree, provided that Zforms an ionic or coordination bond to a cation.
 5. A cationic conductorcomposed of a mixture of a polymer represented by formula (5):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Qrepresents an n+1-valence organic group bonded to R through a singlebond; Z represents a functional group capable of forming an ionic bondto or having coordination ability to a cation; M^(k+) represents ak-valence cation; and n and m are each independently an integer of 1 orlarger, provided that Z forms an ionic or coordination bond to a cation;and a different type of polymer.
 6. A cationic conductor composed of amixture of: a polymer represented by formula (6):

wherein R represents an organic group obtained via polymerization ofmonomer compounds having polymerizable unsaturated linkages; Srepresents an organic group bonded to R; T represents an n+1-valenceorganic group bonded to S through a single bond; Z represents afunctional group capable of forming an ionic bond to or havingcoordination ability to a cation; M^(k+) represents a k-valence cation;and n and m are each independently an integer of 1 or larger, providedthat Z forms an ionic or coordination bond to a cation; and a differenttype of polymer.
 7. The cationic conductor according to claim 2, 4, or6, wherein T in formula (2), (4), or (6) has an aryl group.
 8. Thecationic conductor according to claim 1, 3, or 5, wherein Q in formula(1), (3), or (5) has an aryl group.
 9. The cationic conductor accordingto claim 2, 4, or 6, wherein S in formula (2), (4), or (6) is an amidegroup.
 10. The cationic conductor according to any of claims 1 to 6,wherein Z in formulae (1) to (6) is a hydroxy ion group.
 11. Thecationic conductor according to any of claims 1 to 6, wherein Z informulae (1) to (6) is a methoxy group.
 12. The cationic conductoraccording to any of claims 1 to 6, wherein cation M^(k+) in formulae (1)to (6) is a lithium ion.
 13. The cationic conductor according to any ofclaims 1 to 6, wherein Z in formulae (1) to (6) is a monovalent aniongroup and cation M^(k+) is coordinated to the anion group.
 14. Thecationic conductor according to claim 2, 4, or 6, wherein T comprises anaryl group, S is an amide group, and Z in formula (2), (4), or (6) isbonded to the aryl group at position ortho to a position where the amidegroup is bonded thereto.
 15. The cationic conductor according to claim1, 3, or 5, wherein Q comprises an aryl group, and Z in formula (2),(4), or (6) is bonded to the aryl group at position ortho to a positionwhere R is bonded thereto.
 16. A lithium secondary battery comprising apositive electrode having a positive active material that canintercalate and deintercalate lithium and a negative electrode having anegative active material that can intercalate and deintercalate lithiumthat are wound or laminated via an interposing polymer electrolyte,wherein the polymer electrolyte comprises the cationic conductoraccording to any one of claims 1 to 6.